This paper describes the development of a timer based voltage to frequency converter(V FC).Timer LM555is used in astable multivibrator mode with two OPTO-LDRs(light dependent resistors)in the circuitry.The frequency o...This paper describes the development of a timer based voltage to frequency converter(V FC).Timer LM555is used in astable multivibrator mode with two OPTO-LDRs(light dependent resistors)in the circuitry.The frequency of timer output waveform which is measured using a digital storage oscillator(DSO)is almost linearly proportional to the applied input voltage.Hence we obtain a linear relationship between the frequency of timer output waveform and the input voltage.Because of its quasi-digital output,the main advantages of this developed converter are linear input-output relationship,small size,easy portabilityand high cost performance.In addition,the timer output waveform can be directly interfaced with personal computer or microprocessor/microcontroller for further processing of the input voltage signal without intervening any analog-to-digital converter(ADC).展开更多
在低压配电系统的防雷保护中,对一些敏感设备的过电压保护采用单级SPD通常无法达到雷电防护水平的保护要求,需采用多级SPD配合的方式,才能达到更好的保护效果。在建立两级SPD模型的基础上,考虑了空载、电容负载、电感负载、电阻负载4种...在低压配电系统的防雷保护中,对一些敏感设备的过电压保护采用单级SPD通常无法达到雷电防护水平的保护要求,需采用多级SPD配合的方式,才能达到更好的保护效果。在建立两级SPD模型的基础上,考虑了空载、电容负载、电感负载、电阻负载4种电缆末端负载及不同电缆长度对SPD配合的影响,利用PSCAD仿真软件研究了20 k V/10 k A混合波形作用下两级低压SPD的配合规律。仿真结果表明,在两级SPD保护系统中,前级SPD分流比通常可达60%-100%,承受着相当大部分雷电流,而后级SPD选择不当可能会使残压波形产生较大振荡,由此带来的较大残压幅值或较高振荡频率,对设备会有较大影响。展开更多
文摘This paper describes the development of a timer based voltage to frequency converter(V FC).Timer LM555is used in astable multivibrator mode with two OPTO-LDRs(light dependent resistors)in the circuitry.The frequency of timer output waveform which is measured using a digital storage oscillator(DSO)is almost linearly proportional to the applied input voltage.Hence we obtain a linear relationship between the frequency of timer output waveform and the input voltage.Because of its quasi-digital output,the main advantages of this developed converter are linear input-output relationship,small size,easy portabilityand high cost performance.In addition,the timer output waveform can be directly interfaced with personal computer or microprocessor/microcontroller for further processing of the input voltage signal without intervening any analog-to-digital converter(ADC).
文摘在低压配电系统的防雷保护中,对一些敏感设备的过电压保护采用单级SPD通常无法达到雷电防护水平的保护要求,需采用多级SPD配合的方式,才能达到更好的保护效果。在建立两级SPD模型的基础上,考虑了空载、电容负载、电感负载、电阻负载4种电缆末端负载及不同电缆长度对SPD配合的影响,利用PSCAD仿真软件研究了20 k V/10 k A混合波形作用下两级低压SPD的配合规律。仿真结果表明,在两级SPD保护系统中,前级SPD分流比通常可达60%-100%,承受着相当大部分雷电流,而后级SPD选择不当可能会使残压波形产生较大振荡,由此带来的较大残压幅值或较高振荡频率,对设备会有较大影响。
